Better mixing leads to faster reactions for key chemicals

Pouring cream into coffee creates a show of eddies that rivals Jupiter's roiling storms. But one clank of the spoon collapses all that black and tan chaos into a smooth, uniform brown. It turns out there's a lot to that mixing. ...

How a deadly strain of salmonella fine-tunes its infection tactics

Disease-causing microbes have evolved sophisticated strategies for invading the body, flourishing in often hostile environments and evading immune defenses. In a new study, Professor Cheryl Nickerson, her Arizona State University ...

Modeling a right royal butterfly effect

The monarch butterfly, Danaus plexippus, is renowned for its striking appearance and perhaps even more than that, its remarkable long-distance migration. The population present in North America heads south each year in the ...

Honey bees vote to decide on nest sites—why we should listen

When people think of honey bees, they often think of classic wooden hives, in which beekeepers are having to breed more and more bees just to keep managed populations stable. These man-made boxes, designed to facilitate pollination ...

Observing flows at a liquid-liquid-solid intersection

Most of us are familiar with the classic example of a liquid-gas moving contact line on a solid surface: a raindrop, sheared by the wind, creeps along a glass windscreen. The contact line's movements depend on the interplay ...

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Fluid

In physics, a fluid is a substance that continually deforms (flows) under an applied shear stress, no matter how small. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids.

In common usage, "fluid" is often used as a synonym for "liquid", with no implication that gas could also be present. For example, "brake fluid" is hydraulic oil and will not perform its required function if there is gas in it. This colloquial usage of the term is also common in medicine and in nutrition ("take plenty of fluids").

Liquids form a free surface (that is, a surface not created by the container) while gases do not. The distinction between solids and fluid is not entirely obvious. The distinction is made by evaluating the viscosity of the substance. Silly Putty can be considered to behave like a solid or a fluid, depending on the time period over which it is observed. It is best described as a viscoelastic fluid. There are many examples of substances proving difficult to classify. A particularly interesting one is pitch, as demonstrated in the pitch drop experiment currently running at the University of Queensland.

This text uses material from Wikipedia, licensed under CC BY-SA